Electron Density Map of the Surface of Sindbis Virus (yellow) and the Virus Nucleocapsid (blue).

The surface of  Sindbis virus is made up of 240 copies of each of two virus encoded membrane glycoproteins.  The proteins (E1 &E2) are organized into trimers of E1-E2 pairs.  One of these trimers is seen in the center of the virus structure presented above. 80 of these timers are linked together to form an icosahedral structure.  The proteins E1 and E2 are imbedded into a membrane bilayer which is of host cell origin. The nucleocapsid is also icosahedral in structure and is in its three dimensional organization identical  to the virus surface.  The nucleocapsid is composed of 240 copies of a single protein (C).  The nucleocapsid is attached to the membrane glycoproteins by association with the endodomain of the E2 glycoprotein.  Thus Sindbis virus is composed of two nested protein icosahedral protein shells.  A membrane bilayer is sandwiched between the two shell and the protein shell are linked to one another by proteins which penetrate the membrane. The complex pathway by which this remarkable structure is assembled in side a cell and its disassembly as it infects cells are major thrusts of this research program.

Images provided by our collaborator Dr. Angel Parades Baylor College of Medicine